Solid ink or phase change ink printers conventionally receive ink in a solid form, either as pellets or as ink sticks. The solid ink pellets or ink sticks are placed in a feed chute and a feed mechanism delivers the solid ink to a heater assembly. Solid ink sticks are either gravity fed or urged by a spring through the feed chute toward a heater plate in the heater assembly. The heater plate melts the solid ink impinging on the plate into a liquid that is delivered to a print head for jetting onto a recording medium. U.S. Pat. No. 5,734,402 for a Solid Ink Feed System, issued Mar. 31, 1998 to Rousseau et al.; and U.S. Pat. No. 5,861,903 for an Ink Feed System, issued Jan. 19, 1999 to Crawford et al. describe exemplary systems for delivering solid ink sticks into a phase change ink printer.
Phase change inks for color printing typically comprise a phase change ink carrier composition which is combined with a phase change ink compatible colorant. In a specific embodiment, a series of colored phase change inks can be formed by combining ink carrier compositions with compatible subtractive primary colorants. The subtractive primary colored phase change inks can comprise four component dyes, namely, cyan, magenta, yellow and black, although the inks are not limited to these four colors. These subtractive primary colored inks can be formed by using a single dye or a mixture of dyes. For example, magenta can be obtained by using a mixture of Solvent Red Dyes or a composite black can be obtained by mixing several dyes. U.S. Pat. Nos. 4,889,560, 4,889,761, and 5,372,852, the disclosures of each of which are totally incorporated herein by reference, teach that the subtractive primary colorants employed can comprise dyes from the classes of Color index (C.I.) Solvent Dyes, Disperse Dyes, modified Acid and Direct Dyes, and Basic Dyes. The colorants can also include pigments, as disclosed in, for example, U.S. Pat. No. 5,221,335, the disclosure of which is totally incorporated herein by reference. U.S. Pat. No. 5,621,022, the disclosure of which is totally incorporated herein by reference, discloses the use of a specific class of polymeric dyes in phase change ink compositions.
Ink sticks currently in use are typically manufactured with a formed tub and flow fill process. In this method, the component dyes and carrier composition is heated to its liquid state and then poured into a tub having an interior shape corresponding to the desired finished ink stick shape. The tub may also be formed with indentations and protrusions for forming keying and coding features in the ink sticks, if desired. This manufacturing method allows formation of non-linear shapes, although dimensions for the sticks may vary beyond desired tolerance ranges. Poor height control and stress cracks may be caused by non uniform cooling of the ink. Specifically, the outer layer of the molten ink and carrier radiate heat to the outside air and cool more quickly than the interior portions of the mixture. This situation is worsened by the fact that the upper surface is an open top and cools at a different rate than the tub surround areas on the sides and bottom. Additionally, features cannot be formed in the upper surface with this method. The top surface nearly always solidifies into an uncontrolled, non flat shape such that stick to stick and areas across a stick vary in height. Poor height control can allow sticks to be undesirably displaced during handling and transport and even operation of the printer or imaging device. The flow fill process is used in spite of these limitations because it is very fast and cost effective. The process of extrusion is another method of generating forms with a lot of mass very quickly and economically. Extrusion, however, generates forms that incorporate features in the longitudinal direction only. Features perpendicular to the feed direction cannot be made directly.